Gold mining Environmental Issues

Last month, you explained why green consumers should be cautious when . What if I wanted to buy my wife a simple gold band? What kind of environmental impacts would that have?

A gold band may be the ultimate in effortless style, but it takes a lot of work to produce one. Forget any '49er fantasies you may have of nuggets glittering in riverbeds: Most gold these days comes from large open-pit mines, where huge amounts of rock are churned up to extract tiny flecks of precious metal. A "rich" mine might contain just a few tenths of an ounce of gold per ton of ore; a "poor" one would have a few hundredths of an ounce per ton. The mining watchdog group Earthworks estimates that a standard 18-karat wedding band leaves behind 20 tons of ore and waste rock.

Moving that much earth doesn't just require a lot of energy. It can also lead to toxic mine drainage, probably the biggest environmental concern associated with gold-mining. When you dig up rock that's been buried for a long time, air and moisture can set off chemical reactions that produce acids and leach toxic metals. If those substances - sulfuric acid, arsenic and copper, for example - run off into lakes, rivers and streams, they will pose serious risks for populations of fish and other aquatic organisms. Mine drainage is a problem for many kinds of operations, but it's especially significant for gold extraction. For one thing, gold is often found in rock that contains a lot of acid-generating sulfides; for another, mining gold produces much more unwanted rock than does mining other minerals.

Once you start extracting the gold from the ore, new issues arise. Take mercury, for example. The element, which has been linked to a host of negative health effects, is found in many metal and coal deposits. Large-scale gold operations often start processing ore by roasting it, which can shoot a lot of mercury into the atmosphere. (The same thing happens at coal-burning power plants, the source of about half the United States' airborne mercury emissions in 2005.)

New pollution control technologies can greatly reduce the emissions from gold roasters. For example, according to University of Nevada environmental science professor Glenn Miller, scrubbers have helped Nevada cut its mercury emissions from more than 20, 000 pounds a year a decade ago to just about 4, 000 pounds a year. Meanwhile, there's hope that new treatment processes can also alleviate the serious mercury pollution issues related to small-scale gold-mining in the developing world. According to the EPA, these operations - which produce about one-fifth of the world's gold - are currently the planet's No. 1 source of mercury releases to the environment.

Whether or not they roast the ore, big mining operations typically finish off the extraction process by dousing the ore in cyanide. Cyanide is extremely lethal, but as an environmental contaminant it's not as problematic as mercury, since it degrades fairly quickly. (Mercury sticks around forever.) Some of the byproducts of that degradation process, such as nitrates, may contaminate groundwater, but a bigger issue is that the use of cyanide allows mining companies to go after very low-grade ore. That means they end up digging up more earth to produce the same amount of gold, which produces huge amounts of tailings, the material that's left over once the ore has been processed. Gold tailing ponds and piles are chock-full of contaminants such as arsenic, antimony, residual cyanide and mercury, and so must be carefully managed to avoid generating runoff or coming into contact with wildlife. These tailings can stay toxic for centuries, so proper post-closure plans are crucial.

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